1. Field of the Invention
This invention relates to a wiper driving unit and more particularly to improvements in a wiper home position stop device effective for use in a wiper driving unit mounted on a vehicle such as a motor vehicle which may travel a snowfall zone for example.
2. Description of the Prior Art
In general, in the wiper driving unit mounted on a vehicle such as a motor vehicle, to secure safety in driving, there has been provided an automatic home position stop device capable of moving a wiper blade to a corner of the bottom of a window and stopping it thereat even when a manual control switch is turned off at random.
In the conventional home position stop device of the type described, a conductor plate partially having a non-conductive part is attached to an end face of a driving gear, a switch consituting a switch for opening or closing an electric circuit of a motor in cooperation with the conductor plate is provided on a housing in such a manner that the conductor plate is caused to slide by the rotation of the driving gear. Even when the manual control switch is turned off at random, an electric circuit to the home position is formed by the conductor plate and the contact, a main circuit is shut off at the home position by the non-conductive part of the conductor plate, an armature circuit is short-circuited and an electric brake is applied, whereby a wiper motor is automatically stopped.
However, the wiper driving unit provided with the above-described home position stop device presents such disadvantages that, when an external force working in a direction opposite to the normal rotation is applied to the driven gear as in the case where snow is scraped up to the bottom portion of a front window of a motor vehicle for example, a chattering phenomenon of repeating continuity and discontinuity is generated in a portion between the conductor plate and the contact, whereby deterioration due to the generation of heat, lowering of durability and the like are caused to the aforesaid portion.